1. Field of the Invention
This invention relates to a contactless IC card, a responding method, and a program therefor, and more specifically relates to the contactless IC card, the responding method, and the program that respond to a request sent from a reader/writer by means of a time slot.
2. Prior Art of the invention
Generally, it is the time slot system that is applied to the communication between a contactless IC card and a reader/writer; the contactless IC card for sending and receiving data by means of the electromagnetic induction method; and the reader/writer for recognizing the contactless IC card. The reason for adopting the time slot is that a plurality of contactless IC cards exist simultaneously within a communication area of a reader/writer, and then the plurality of contactless IC cards respond to the polling of the reader/writer simultaneously, in which case any contactless IC card cannot communicate with the reader/writer normally because each response signal used for the response is in collision with one another.
The communication method of the time slot system will be described hereafter.
(1) In order to recognize existence of contactless IC card, the reader/writer sends an initial response request command to the contactless IC card as a request. The initial response request command contains “the number of slots” that is required to control the time (time slot) to make an initial response to the request executed by the contactless IC card, or a value that is required to calculate “the number of slots”.
(2) The contactless IC card sends back the initial response to the request at a time slot (one of 1 to “the number of slots”) of a specific time set after receiving the request in response to the initial response request command. The time slot used for response, which is a period between specific times, is decided by the card itself on the basis of a random numbers.
(3) If it is detected the collision of initial responses that appear when a plurality of contactless IC cards select a same time slot, the reader/writer resends an initial response request.
(4) The reader/writer recognizes all the contactless IC cards by receiving the initial responses from all the contactless IC cards without collision, and then the sequence for identifying the contactless IC cards is completed.
The following explains in more detail about the above-mentioned processing according to FIG. 16 to FIG. 18. Besides, the following processing is concerned with the contactless IC card adjusted to the international standard ISO/IEC14443 for the proximity contactless IC card.
For instance, ISO/IEC14443 can be applied to a contactless Telephone Card. More specifically, it is a case where that contactless IC cards 1601 and 1602 having a function of telephone card are simultaneously put into a reader/writer functioning as a payphone, which is shown as FIG. 16.
The recognition system of the contactless IC card of ISO/IEC14443 executes the recognition of the contactless IC card according to the following procedure.
First, the reader/writer 1600 as the payphone sends an initial response request (request). The initial response request has a format shown in FIG. 18 and notifies the contactless IC card of the number of time slots (N) by means of three bits 1803 composed of bit 1 to bit 3, those bits included in 8 bits of PARAM 1802 composing the initial response request 1801. Besides, APf 1804 is a header indicating the initial response request command, while AFI 1805 indicates an adaptive class of the contactless IC card. And CRC (Cyclic Redundancy Check) 1806 is CRC from APf to PARAM.
Besides the contactless IC card responds to the initial response request at one of N slots of 1 to N, however, the following explanation is made on the basis that the number of time slots (N) is assumed to 4. That is to say, the contactless IC cards 1601 and 1602 select a time slot from 1 to 4 slots, and make the initial response.
In a first card identification processing 1701 shown in FIG. 17, an initial response request R1[REQB] (1702) is sent from the reader/writer 1600. When the contactless IC cards 1601 and 1602 generate “1” respectively as a random number in response to the initial response request R1 (1702), the respective responses are made as the initial responses [ATQB] A21 and A31 within the time slot 1 (1704). In this case, since both the contactless IC cards 1601 and 1602 send the initial responses simultaneously at the same time, the reader/writer 1600 detects the collision of the initial responses of the contactless IC cards. Accordingly, the reader/writer 1600 starts the identification processing again.
In a second identification processing 1707, an initial response request R2 (1703) is sent from the reader/writer 1600. When the contactless IC cards 1601 and 1602 generates “3” and “2” respectively in response to the initial response request, the responses are made by packets A22 sent within the time slot 3 (1705) and packets A32 sent within the time slot 2 (1706) respectively. In this case, since the reader/writer 1600 does not detect the collision, the reader/writer can identify all the contactless IC cards, and then the identification processing is completed. The above processing is the identification of contactless IC card adaptive to the ISO/IEC 14443 standard. Under the ISO/IEC 14443 standard, the period between when the contactless IC card receives the initial response request command and when it responds to the request at the time slot 1 is defined as 302 μsec, and the period of a time slot is as 2266 μsec. The period (μsec), from when the contactless IC card receives the initial request from the reader/writer 1600 to when the card sends the initial response, can be found according to the following equation (Equation 1).Period (μsec)=302 μsec+2266 μsec×(the selected number of slots−1)  EQUATION 1
As one of such systems, the wireless identification device (Japanese laid-open publication No. 9-6934) is disclosed, and there is the slot maker system as the other similar system to the time slot system.
The slot marker system is a method in which, the reader/writer sends an initial-response request using the time-slot method, and then sends a slot marker command at the timing of the start of each slot, which indicates the start of the slot. Each IC card responds by using the time slot specified by the reader/writer, so the aspect of identifying IC cards is essentially the same as in the time-slot method.
Under the wireless identification device (Japanese laid-open publication No. 9-6934) or the contactless IC card compliant with International Standard ISO/IEC14443, when the contactless IC card responds to the reader/writer, the contactless IC card itself selects the time slot by means of random numbers, and the contactless IC card response during a specific time interval specifying the time slot. Therefore, for instance, where random numbers generated by a plurality of contactless IC cards are the same one, the selected time slots are the same and the initial response requests never fail to come into collision. In this case, it is necessary for the reader/writer to send the initial response request command again and recognize the contactless IC card. It causes to delay the recognition of the contactless IC card.
By increasing the number of time slots that the reader/writer allocates for the contactless IC card, it is possible to decrease the probability that the plurality of contactless IC cards select the same time slot. However, as the time slot increases in number, the time for completing (terminating) the response to the initial response request at all the time slots comes to be longer. In results, it takes a lot of time for the reader/writer to complete the recognition of the contactless IC card.
The above-mentioned problem, that it takes a lot of time to complete the recognition, appears remarkably in the system such as a ticket examining machine at a wicket, wherein the user has to let the reader/writer recognize the contactless IC card without stopping. That is to say, if the recognition of contactless IC card is delayed, the use has to stop and it becomes an obstacle in the utilization of the system.
Additionally, if it is possible to recognize the contactless IC card speedier than ever, the system will be able to be applied to a speedier mobile device. For this purpose, it has been expected to improve the speed-up of the recognition and the processing.